The present invention relates to a photosensitive resin composition which is used as a solder resist in printed circuit boards, can be satisfactorily developed in a dilute basic aqueous solution and can yield a cured film that is excellent in flexibility, water resistance, adhesion, solder heat resistance, electroless gold plating resistance, pressure cooker test (PCT) resistance and other properties.
To pattern resists on printed circuit boards, screen printing has been conventionally used in many cases. However, a photosensitive resin that can be developed in a dilute basic solution as described in Japanese Examined Patent Application Publication No. 1-54390 is now used to improve productivity. This photosensitive resin is a novolak epoxy (meth)acrylate that has a carboxyl group in a side chain and is obtained by allowing acrylic acid as an unsaturated monobasic acid to react with a novolak epoxy resin and allowing a saturated or unsaturated polybasic acid anhydride to react with the resulting hydroxyl group.
With increasing performances of electronic equipment, further downsized semiconductor packages have been launched in mass production. For example, ball grid arrays (BGAs), chip size packages (CSPS) and other semiconductor packages are now commercially available.
These BGAs, CSPs and other parts are packed by heating a whole work with infrared ray irradiation and reflowing solder to fix the parts. In this procedure, conventional solder resist films as described in Japanese Examined Patent Application Publication No. 1-54390 may cause defects such as cracking due to heat shock. Demands are therefore made on resist films that have improved impact resistance, adhesion, solder heat resistance, electroless gold plating resistance, PCT resistance and other properties.
Japanese Unexamined Patent Application Publication No. 6-324490 discloses a photosensitive resin which is obtained by allowing a novolak epoxy resin to react with dimethylolpropionic acid having two or more hydroxyl groups per molecule and acrylic acid as an unsaturated monobasic acid, and allowing the resulting product to react with a saturated or unsaturated polybasic acid anhydride. A cured product of this type of photosensitive resins may comprise hydroxyl groups in excess and may therefore exhibit insufficient PCT resistance due to its deteriorated water resistance, since the amount of the added saturated or unsaturated polybasic acid anhydride is less than that of the hydroxyl group of dimethylolpropionic acid, although it has excellent adhesion, solder heat resistance and electroless gold plating resistance. If the amount of saturated or unsaturated polybasic acid anhydride is increased to relatively decrease the amount of hydroxyl groups, the carboxyl groups are in excess to thereby cause insufficient PCT resistance in some cases. The use of an acid having two or more hydroxyl groups, such as dimethylolpropionic acid, induces excess of one of the hydroxyl group and carboxyl group over another and is not preferred.
Accordingly, an object of the present invention is to provide a photosensitive resin composition which is used as a solder resist in printed circuit boards, can be satisfactorily developed in a dilute basic aqueous solution and can yield a cured film that is excellent in flexibility, water resistance, adhesion, solder heat resistance, electroless gold plating resistance and pressure cooker test (PCT) resistance.
After intensive investigations, the present inventors have solved the conventional problems.
Specifically, the present invention provides a photosensitive resin composition comprising:
(A) a photosensitive resin;
(B) an epoxy resin;
(C) a photopolymerization initiator; and
(D) a polymerizable unsaturated compound and/or a solvent,
in which the photosensitive resin (A) is obtained by allowing an epoxy resin (a) to react with a compound (b) having one primary alcoholic hydroxyl group and one functional group selected from a carboxyl group and a secondary amino group per molecule, and an unsaturated monobasic acid (c) to yield a reaction product (I) and allowing a saturated or unsaturated polybasic acid anhydride (d) to react with the hydroxyl group of the reaction product (I).
The photosensitive resin (A) in the photosensitive resin composition may be obtained by allowing from 0.6 mole to 1.0 mole inclusive of the saturated or unsaturated polybasic acid anhydride (d) to react with 1 mole of the primary hydroxyl group of the reaction product (I).
In the photosensitive resin (A) of the photosensitive resin composition, 0.8 to 1.2 equivalent weight in total of the compound (b) and the unsaturated monobasic acid (c) including 0.05 to 0.5 equivalent weight of the compound (b) may be allowed to react with 1 equivalent weight of epoxy groups of the epoxy resin (a).
The photosensitive resin composition may comprise 1% to 50% by weight of the epoxy resin (B) based on the total weight of the composition.
The photosensitive resin composition may comprise 0.5% to 20% by weight of the photopolymerization initiator (C) based on the total weight of the composition.
Preferably, the photosensitive resin composition comprises 5% to 80% by weight of the polymerizable unsaturated compound and/or solvent (D) based on the total weight of the composition.
The present invention will be illustrated in further detail below.
Photosensitive resins (A) for use in the present invention are obtained by allowing an epoxy resin (a) to react with a compound (b) having one primary alcoholic hydroxyl group and one functional group selected from a carboxyl group and a secondary amino group per molecule, and an unsaturated monobasic acid (c) to yield a reaction product (I) and allowing a saturated or unsaturated polybasic acid anhydride (d) to react with the hydroxyl group of the reaction product (I).
Examples of the epoxy resin (a) include epoxy resins such as cresol novolak epoxy resins, phenol novolak epoxy resins, dicyclopentadiene-phenol polyaddition epoxy resins and combinations of these resins. These novolak epoxy resins may be halogenated.
Part of such cresol novolak epoxy resins, phenol novolak epoxy resins, dicyclopentadiene-phenol polyaddition epoxy resins may be substituted with other epoxy resins within ranges not deteriorating the advantages of the present invention. Such other epoxy resins include, but are not limited to, bisphenol A epoxy resins, bisphenol F epoxy resins, hydrogenated bisphenol A epoxy resins, phenol-cresol co-condensation epoxy resins, bisphenol A novolak epoxy resins, bisphenol F novolak epoxy resins, triphenylolmethane epoxy resins, tetraphenylolethane epoxy resins and other epoxy resins prepared by allowing polyfunctional phenols to react with epichlorohydrin, epoxy resins prepared by allowing polyfunctional hydroxynaphthalenes to react with epichlorohydrin, silicone-modified epoxy resins, xcex5-caprolactone-modified epoxy resins, glycidylamine epoxy resins prepared by allowing epichlorohydrin to react with primary or secondary amines, triglycidyl isocyanate and other heterocyclic epoxy resins.
Examples of the compound (b) having one primary alcoholic hydroxyl group and one functional group selected from a carboxyl group and a secondary amino group include glycolic acid, 16-hydroxyhexadecanoic acid and other compounds each having a primary alcoholic hydroxyl group and a carboxyl group; N-benzylethanolamine and other compounds each having a primary alcoholic hydroxyl group and a secondary amino group, of which glycolic acid is typically preferred.
The alcoholic hydroxyl group of the compound (b) is a primary hydroxyl group and has a higher reactivity with respect to the saturated or unsaturated polybasic acid anhydride (d) than a secondary hydroxyl group. Such a secondary hydroxyl group is formed by the reaction of the epoxy group of the epoxy resin (a) with the carboxyl group or secondary amino group of the compound (b) or with a carboxylic acid radical of the unsaturated monobasic acid (c). The saturated or unsaturated polybasic acid anhydride (d) therefore preferentially react with the primary hydroxyl group rather than the secondary hydroxyl group. This photosensitive resin (A) can yield a cured product that has crosslinking points at longer intervals and is more flexible with higher developing property than cured products of conventional photosensitive resins as described in Japanese Examined Patent Application Publication No. 1-54390. Such conventional photosensitive resins are obtained by allowing a novolak epoxy resin to react with acrylic acid as an unsaturated monobasic acid and allowing a saturated or unsaturated polybasic acid anhydride to react with the formed secondary hydroxyl group.
Based on the above mechanism, when the saturated or unsaturated polybasic acid anhydride is added in a number of moles higher than that of the primary hydroxyl group, a primary hydroxyl group derivative in equivalent mole to that of the primary hydroxyl group is always formed, and the cured product of the resulting composition exhibits high flexibility. However, if the amount of the added saturated or unsaturated polybasic acid anhydride is excessively high (if it exceeds 0.7 mole relative to 1 mole of the total hydroxyl group of the reaction product (I)), the cured product exhibits deteriorated PCT resistance. The amount of the saturated or unsaturated polybasic acid anhydride to be added is preferably less than or equal to 0.7 mole, relative to 1 mole of the total hydroxyl groups of the reaction product (I). More preferably, the amount is equal to or more than 0.6 mole and less than or equal to 1.0 mole relative to 1 mole of the primary hydroxyl group of the reaction product (I). If the amount is less than 0.6 mole, the hydroxyl group becomes excessive to thereby deteriorate PCT resistance and developing property.
The unsaturated monobasic acid (c) is a monobasic acid having one carboxyl group and one or more polymerizable unsaturated bonds, of which acrylic acid and methacrylic acid are preferred. Acrylic acid is typically preferred to yield high curability with active light or radiant rays. In addition, such unsaturated monobasic acids include crotonic acid, cinnamic acid, sorbic acid, acrylic acid dimer, monomethyl maleate, monopropyl maleate, monobutyl maleate, and polyfunctional carboxyl-group-containing acrylates or methacrylates which are reaction products of polyfunctional acrylates or methacrylates each having one hydroxyl group and one or more acryloyl groups with dibasic acids among polybasic acid anhydrides mentioned below. Each of these unsaturated monobasic acids can be used in combination.
In the reaction among the epoxy compound (a), the compound (b) and the unsaturated monobasic acid (c), preferably about 0.8 to about 1.2 equivalent weight, and more preferably about 0.9 to about 1.1 equivalent weight, of the total of the compound (b) and the unsaturated monobasic acid (c) is allowed to react with 1 equivalent weight of the epoxy group of the epoxy compound (a). In this reaction, the amount of the compound (b) is preferably 0.05 to 0.5 equivalent weight relative to 1 equivalent weight of the epoxy group of the epoxy compound (a).
In the reaction, a diluent is preferably used. Such diluent include, but are not limited to, methyl ethyl ketone, cyclohexanone and other ketones; toluene, xylene, tetramethylbenzene and other aromatic hydrocarbons; dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether and other glycol ethers; ethyl acetate, butyl cellosolve acetate, carbitol acetate and other esters; octane, decane and other aliphatic hydrocarbons; petroleum ether, petroleum naphtha, hydrogenated petroleum naphtha, solvent naphtha and other petroleum solvents and other organic solvents, as well as carbitol (meth)acrylate, pentaerythritol tetra(meth)acrylate, trimethylolpropane (meth)acrylate, tris(hydroxyethyl) isocyanurate tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate and other reactive monomers. In addition, a catalyst is preferably used to accelerate the reaction. Such catalysts include, for example, triethylamine, benzyldimethylamine, methyltriethylammonium chloride, benzyltrimethylammonium bromide, benzyltrimethylammonium iodide, triphenylphosphine, triphenyl stibine, chromium octanoate and zirconium octanoate. The amount of the catalyst is preferably 0.01% to 1% by weight relative to the weight of the reaction material mixture. The reaction is preferably performed at 60xc2x0 C. to 150xc2x0 C. for 5 to 60 hours. Thus, the reaction product (I) can be obtained.
Preferred examples of the saturated or unsaturated polybasic acid anhydride (d) are maleic anhydride, succinic anhydride, itaconic anhydride, phthalic anhydride, tetrahydrophthalic anhydrous, hexahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, chlorendic anhydride and other dibasic acid anhydrides; trimellitic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic anhydride, biphenyltetracarboxylic anhydride and other polybasic acid anhydrides. Among them, tetrahydrophthalic anhydride, succinic anhydride and hexahydrophthalic anhydride are typically preferably used.
The reaction is preferably performed at 60xc2x0 C. to 150xc2x0 C. for 1 to 10 hours.
The content of the photosensitive resin (A) in the composition of the present invention is preferably 10% to 80% by weight and more preferably 15% to 60% by weight based on the total weight of the composition.
The epoxy resin (B) is a thermosetting component and has one or more epoxy groups per molecule. Such epoxy resins include, for example, bisphenol A epoxy resins, bisphenol F epoxy resins, hydrogenated bisphenol A epoxy resins, phenol novolak epoxy resins, cresol novolak epoxy resins, dicyclopentadiene-phenol novolak epoxy resins, phenol-cresol novolak co-condensation epoxy resins, bisphenol A novolak epoxy resins, bisphenol F novolak epoxy resins or halogenated epoxy compounds of these resins, triphenylolmethane epoxy resins, alkyl-substituted triphenylolmethane epoxy resins, tetraphenylolethane epoxy resins and other epoxy resins obtained by allowing polyfunctional phenols to react with epichlorohydrin, epoxy resins obtained by allowing polyfunctional hydroxynaphthalenes to react with epichlorohydrin, silicone-modified epoxy resins, xcex5-caprolactone-modified epoxy resins, glycidylamine epoxy resins obtained by the reaction between epichlorohydrin and primary or secondary amines, triglycidyl isocyanate and other heterocyclic epoxy resins. Each of these epoxy resins (B) can be used alone or in combination.
The epoxy resins (B) are used to improve properties as the solder resist, such as adhesion, heat resistance and plating resistance.
Each of the epoxy resins (B) is used alone or in combination as a mixture, and the amount of the epoxy resins (B) in the composition of the present invention is preferably 1% to 50% by weight and more preferably 3% to 45% by weight based on the total weight of the composition.
The epoxy resin (B) is preferably used in combination with an epoxy curing agent in order to further improve adhesion, chemical resistance, heat resistance and other properties. Such epoxy curing agents include, for example, imidazoles, amines, guanamines, polyamines, triazine derivatives, tertiary amines, polyphenols, organophosphines, phosphonium salts, quaternary ammonium salts, and photocationic polymerization catalysts. Examples of such epoxy curing agents are imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1-benzyl-2-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 2-phenyl-4,5-bis(hydroxymethyl)imidazole and 2-alkylformylimidazoles; guanamines such as acetoguanamine and benzoguanamine; amines such as diaminodiphenylmethane, m-phenylenediamine, m-xylylenediamine, diaminodiphenyl sulfone, dicyandiamide, urea and urea derivatives; guanamines such as acetoguanamine and benzoguanamine; polyamines such as melamine, polybasic hydrazide, or organic acid salts and/or epoxy adducts of these compounds, and boron trifluoride amine complex; triazine derivatives such as ethylamino-S-triazine, 2,4-diamino-S-triazine, 2,4-diamino-S-triazine and 2,4-diamino-6-xylyl-S-triazine; tertiary amines such as trimethylamine, triethanolamine, N,N-dimethyloctylamine, N-benzyldimethylamine, pyridine, N-methylmorpholine, hexa(N-methyl)melamine, 2,4,6-tris(dimethylaminophenol) and tetramethylguanidine; polyphenols such as polyvinylphenol, polyvinylphenol bromides, phenol novolaks, and alkylphenol novolaks; organophosphines such as tributylphosphine, triphenylphosphine and tris-2-cyanoethylphosphine; phosphonium salts such as tri-n-butyl(2,5-dihydroxyphenyl)phosphonium bromide, hexadecyltributylphosphonium bromide and hexadecyltributylphosphonium bromide; quaternary ammonium salts such as benzyltrimethylammonium chloride, phenyltributylammonium chloride and other derivatives; as well the aforementioned saturated or unsaturated polybasic acid anhydrides, diphenyliodonium tetrafluoroborate, triphenylsulfonium hexafluoroantimonate, 2,4,6-triphenylthiopyridinium hexafluorophosphate, iron-arene complexes and other photocationic polymerization catalysts; conventional curing agents or curing accelerators for use in the reaction of styrene-maleic acid resin. Each of these compounds can be used alone or in combination. The amount of the epoxy resin curing agent is preferably 0.01 to 25 parts by weight and more preferably 0.1 to 15 parts by weight relative to 100 parts by weight of the epoxy resin (B).
The photopolymerization initiator (C) includes, for example, benzoins, acetophenones, anthraquinones, thioxanthones and benzophenones. Examples of these compounds are benzoins such as benzoin and benzoin methyl ether, benzoin isopropyl ether and other benzoin derivatives; acetophenones such as acetophenone, 2,2-dimethoxy-2-phenylacetophenone and other acetophenone derivatives; anthraquinones such as 2-methylanthraquinone, 2-chloroanthraquinone, 2-ethylanthraquinone, 2-t-butylanthraquinone, and other anthraquinone derivatives; thioxanthones such as thioxanthone, 2,4-dimethylthioxanthone and other thioxanthone derivatives; benzophenones such as benzophenone, 4-benzoyl-4xe2x80x2-methyldiphenyl sulfide, 4,4xe2x80x2-dichlorobenzophenone, N,N-dimethylaminobenzophenone and other benzophenone derivatives, as well as 2,4,6-trimethylbenzoyldiphenylphosphine oxide. Each of these compounds can be used alone or in combination. The photopolymerization initiator (C) can be used in combination with one or more types of photosensitizers such as tertiary amines. Such tertiary amines include, for example, ethyl N,N-dimethylaminobenzoate, isoamyl N,N-dimethylaminobenzoate, pentyl-4-dimethylaminobenzoate, triethylamine and triethanolamine.
Preferably, 2-ethyl-1-[4-(methylthio)phenyl]-2-morpholinolpropan-1-one is used in combination with at least one selected from 2,4-diethylthioxanthone, 4-benzoylthioxanthone and 2-isopropylthioxanthone.
The amount of the photopolymerization initiator (C) is preferably 0.5% to 20% by weight and more preferably 1% to 10% by weight based on the total weight of the composition of the present invention.
As a diluent, the polymerizable unsaturated compound and/or solvent (D) can be used. This component is used in order to improve coatability when a curable and/or photosensitive resin composition with respect to active light or radiant ray is used as a resist ink.
As such polymerizable unsaturated compounds, monomers that can be cured with active light or radiant ray are preferred. Such monomers include, for example, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, isoamyl acrylate, butoxyethyl acrylate, methoxypolyethylene glycol acrylate, ethoxypolyethylene glycol acrylate, melamine acrylate, phenoxyethyl acrylate, phenoxypropyl acrylate, ethylene glycol diacrylate, dipropylene glycol diacrylate, poly(dipropylene glycol diacrylate), phenyl glycidyl ether acrylate-tolylene diisocyanate urethane prepolymer, PO-modified bisphenol A diacrylate, N-pyrrolidone, N-acryloylmorpholine, N,N-dimethylacrylamide, N,N-diethylacrylamide, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminopropyl acrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, glycerol diacrylate, isobornyl acrylate, dicyclopentenyloxyethyl acrylate, and methacrylates corresponding to these acrylates. Each of these polymerizable unsaturated compounds can be used alone or in combination.
The solvents include, for example, ketones, aromatic hydrocarbons, carbitols and acetates. Examples of such solvents are ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene and xylene; carbitols such as ethyl cellosolve, butyl cellosolve, carbitol and butyl carbitol; acetates such as ethyl acetate, butyl acetate, cellosolve acetate, butyl cellosolve acetate and carbitol acetate. Each of these solvents can be used alone or in combination.
Each of the polymerizable unsaturated compounds and/or solvents (D) can be used alone or in combination as a mixture. The amount of the component (D) is preferably from 5% to 80% by weight and more preferably from 10% to 70% by weight based on the total weight of the photosensitive resin composition of the present invention.
When the photosensitive resin composition of the present invention is used as a liquid resist ink, it may further comprise additives according to necessity. Such additives include, for example, silica, calcium carbonate, barium sulfate, clay, talc and other inorganic fillers; phthalocyanine green, phthalocyanine blue, titanium oxide, carbon black and other coloring pigments; defoaming agents; and leveling agents; as well as hydroquinone, resorcinol, catechol, pyrogallol, hydroquinone monomethyl ether, t-butylcatechol, phenothiazine and other polymerization inhibitors. The amount of these additives is preferably 0% to 60% by weight and more preferably 5% to 40% by weight based on the total weight of the photosensitive resin composition of the present invention.
The photosensitive resin composition may further comprise copolymers of ethylenically unsaturated compounds, polyester resins and other conventional binder resins; polyester (meth)acrylate, polyurethane (meth)acrylate, epoxy (meth)acrylate and other unsaturated group-containing polymerizable oligomers, within ranges not adversely affecting the properties as a solder resist.
The photosensitive resin composition of the present invention is obtained by compounding the individual components preferably in the aforementioned proportions and homogeneously blending them using, for example, a triple roll mill.
The photosensitive resin composition of the present invention is cured, for example, in the following manner and thereby yields a cured product. Specifically, the composition of the present invention is applied onto a printed circuit board to a thickness of 10 to 160 xcexcm by screen printing, spraying, roll coater coating, electrostatic painting, curtain coating or another technique, the resulting film is dried at 60xc2x0 C. to 110xc2x0 C., a negative film is brought into direct contact with the film or is placed on the film without contact, the film is then irradiated with ultraviolet rays, the unexposed portions of the film are then dissolved and removed (developed) with a dilute basic aqueous solution (e.g., 0.5% to 2% sodium carbonate aqueous solution or sodium hydroxide aqueous solution), and the film is further sufficiently cured by ultraviolet rays irradiation and/or heating (e.g., heating at 100xc2x0 C. to 200xc2x0 C. for 0.5 to 1.0 hour) to further improve the physical properties and thereby yields a cured film.
The present invention will be illustrated in further detail with reference to several examples and comparative examples below. All parts and percentages are by weight unless otherwise specified.